 |
| Picture 8. A simplified dialysis
machine. The dialysis solution flows left to right and the blood
flows in the opposite direction. |
|
|
| What is dialysis? |
 |
In dialysis, a patient's blood is passed through a dialysis
machine. The dialysis machine takes over the job of their kidneys,
removing waste products from the blood. |
| How does dialysis work? |
|
Picture 8 shows a simplified diagram of a kidney dialysis
machine.
- a tube connects a person's vein
to the dialysis machine
- inside the machine, blood is pumped through tubes
made from dialysing membranes
- dialysis solution is on the other side of the dialysing
membrane, kept fresh by a constant flow
- blood returns to the person's arm
|
|
|
|
 |
| Picture 9. Diffusion makes the
concentrations the same on both sides of the membrane. |
|
|
|
The dialysing membrane allows small particles to pass
through it. The result is that the concentration of these small particles
will end up being the same
on both sides of the membrane. This is called diffusion.
Let's see how it happens.
The particles are moving
randomly. They can pass both ways through the membrane. However,
more
particles will meet the membrane on the side with a higher concentration.
Therefore more particles will pass through from this side. This
means that there will be a net
flow from the higher concentration to the lower concentration.
This continues until the concentrations are the same.
Then there will be the same
number of particles passing both ways.
|
| Transferring substances |
|
The dialysis solution contains water, glucose,
salts and various substances at the correct concentration for the
body. These substances diffuse through the membrane and into the
blood. So the blood leaving the machine has all these substances
in the same concentration as the dialysis solution.
The fresh dialysis solution does not contain urea - so urea (and
other impurities) pass out of the blood. They are taken away by
the flow of dialysis solution.
Proteins
and blood cells are too big to pass through the membranes so stay
in the blood.
|
|
 |
| Picture 10. Human organs being
transported for transplant
surgery. They have to be kept cool and protected from shocks. |
|
|
| Dialysis on the move – CAPD |
|
CAPD (continuous ambulatory peritoneal
dialysis)
is another sort of dialysis. CAPD uses the body’s own membrane
for dialysis. Dialysis actually goes on inside the patient’s
body. The good thing about it is that dialysis happens all the
time, even when someone is sleeping or out shopping. |
|
|
|
|
|
